Kenyan filmmakers detained by police allegedly had spyware installed on their phones, a press freedom group said Wednesday, saying it was “gravely alarmed” by the move.

Four independent filmmakers — Nicholas Wambugu Gichuki, Bryan Adagala, Mark Karubiu and Chris Wamae — were arrested on May 2 in capital Nairobi and charged with “publishing false information”.

The men were released a day later without charge, but their devices — including their phones, hard drives and laptops — were kept by police until July 10.

The Committee for the Protection of Journalists (CPJ) quoted a researcher at Toronto University’s Citizen Lab, which tracks digital threats against civil society, who said spyware had been installed on devices belonging to two of the detained reporters.

Such software would give “the operators silent, secret access to all sorts of private business and information about their journalism” the senior researcher told CPJ.

“The installation of spyware on Kenyan filmmakers’ devices while in police custody is outrageous,” CPJ Program Director Angela Quintal said, urging authorities to explain “without delay”.

The analysis from Citizen Lab showed that reporters’ devices were unsafe with police, she said in a statement.

Quintal said the “alarming” discovery “further stains the country’s once-lauded reputation for press freedom”.

Citizen Lab documents shared with reporters showed the phones belonged to Wambugu and Adagala.

AFP has contacted the police and ministry of interior over the allegations. It had not heard back by publication.

Activists had linked the filmmakers’ detention with a BBC documentary about security service killings during anti-government protests last year, despite the BBC saying none of the men was involved in the film, “Blood Parliament”.

At least 60 people were killed during weeks of protests that began in June last year over tax rises in a finance bill from the government of President William Ruto.